1. Field of the Invention
The present invention relates to a latch for alternatively preventing the opening of a door or allowing the door to be opened only a limited distance.
2. Prior Art
Door latches to enable one on the inside of a building or living space to open a door a limited distance and converse with one standing outside the door while deterring the outsider from forcibly gaining access to the building or living space have been of the chain guard type. A chain has one end anchored to the doorjamb and the other end engageable with a keeper attached to the door. Because such latches are easily broken by forcing the door and because an outsider can easily reach through a doorway with a device such as a length of wire and disengage the chain from the keeper, or can simply cut the chain with a bolt cutter, the chain guard type of latch has provided limited security. To improve its utility, a key-operated tumbler lock has been incorporated in the keeper. This type of lock may provide increased security but always requires a key to engage or disengage the chain from the keeper.
To ensure against unauthorized entry, a lock only operable from the inside of a door, such as a sliding bolt type or hasp type, is often used in conjunction with a chain guard type lock. This multiplicity of locking devices results in increased costs and detracts from physical appearance. A sliding bolt lock has been incorporated in a chain guard lock in U.S. Pat. No. 3,788,107, but an additional key-operated tumbler lock is still required to ensure that the chain is not disengaged from the keeper by an outsider.